Photorefractive applications

In earlier investigations by the author [1,2] an additional nonlinear optical chromophore, (IV), and charge transport agent, (V), respectively, were prepared and used in photorefractive applications. 

S.R. Marder, B. Kippelen, A.K.Y. Jen, N. Peyghambarian, Design and Synthesis of Chromophores and Polymers for Electro-Optic and Photorefractive Applications , Nature, 388, 845 (1997)... 

Based on the BOA theory, Barzoukas and Blanchard-Desce developed a two-state two-form model for the Pq of push-pull compounds [48]. The y o was expressed as a function of the newly defined parameter MIX, which is related to the degree of mixing between the neutral and zwitterionic resonance forms in the ground and excited state. This treatment has the advantage of conceptual simplicity and that it relies on a structural parameter that can be more easily used for other push pull molecular systems than polyenes. The evolution of y o observed with MIX is identical to that with BOA. The BOA theory was later also used to optimize the figure-of-merit of dyes for photorefractive applications [49, 50]. 

Fig. 4. Schematics of push-pull molecules for electro-optic and photorefractive applications...

By applying this approach new molecules for electro-optic and photorefractive applications could be developed. For a review of the design of nonlinear molecules using the BLA model see for instance [19]. 

Examples of polymers used in photorefractive applications are shown in Fig. 22. PVK and PSX both contain the carbazole moiety that has a donor-like character and provides for hole transport. Carbazole and some other hole transporting moieties have been widely used in the field of photorefractive polymers. The polarity of carbazole makes PVK a good matrix for a lot of the guest electro-active molecules. The choice of a polymer matrix is often dictated by its compatibility with... 

Fig.24a-e. Examples of bifunctional chromophores for photorefractive applications a N-2-butyl-2,6-dimethyl-4H-pyridone-4-ylidenecyanomethylacetate (2BNCM) b 1,3-dimethyll-2,2lctramethylene-5- nit roben zirnidazoli ne (DTNBl) c 4- (N,N -diphenylamino)- (P )-nitros-tyrene (DPANST) d 4,4 -di(N-carbazolyl)-4"-(2-N-ethyl-4-[2-(4-nitrophenyl)-l-azo]anili-noethoxyl-triphenylamine (DRDCTA) e carbazole trimer... 

KIPPELEN ETAL. Organic Polymers for Photorefractive Applications 221... 

Tamura K, Padias AB, Hall Jr HK, Peygham-barian N. New polymeric material containing the tricyanovinylcarbazole group for photorefractive applications. Appl Phys Lett 1992 60 1803-5. 

The TDHF approximation has been employed in conjunction with the PM3 semi-empirical formalism in work by Kim et on the /S-hyperpolarizabilities of photoconductive chromophores. It was noted that the optical non-linearities of dipolar photoconductive molecules with carbazole, indole or indoline as donor units are large enough to be useful in electro-optic and photorefractive applications. 

Fig. 1. Schematic of the photorefractive process. Note the phase shift, (j), between the incident intensity grating and the resulting photorefractive grating in the material. Depending upon the trapping depth and depth of modulation of the intensity of light incident on the material, the phase shift can vary between 0 and ti/2. The absence of this phase shift indicates that mechanisms of photoinduced refractive index change other than photorefraction are involved. Many photorefractive applications require phase shifts approaching jt/2.

A small molecular system based on carbazole moiety was developed for photorefractive applications. One of the molecules has b n shown to form staUe and amorphous films and exhibit good photorefractive performance. A net optical gain of 11 cm- was observed. An attractive feature of this molecule is that its photorefractive response is fast. Because of its structural versatility, this molecular system is worth further exploration. 

Methodology for the Synthesis of New Multifunctional Polymers for Photorefractive Applications... 

Progress in the research on polymers for photorefractive applications during the past 4 years has been encouraging. In addition to the material properties addressed above, however, photorefractive polymers must demonstrate other properties such as good optical quality, reproducibility, stability, processibility, and long grating... 

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